This application relates to a refrigerant system wherein a single line leading into the compressor provides both the unloader function and the economizer or so-called vapor injection function, and wherein a restriction is placed on the economizer injection line at a location such that the unloader function is not affected.
Refrigerant systems are utilized to control the temperature and humidity of air in various indoor environments to be conditioned. In a typical refrigerant system operating in a cooling mode, a refrigerant is compressed in a compressor and delivered to a condenser (or an outdoor heat exchanger in this case). In the condenser, heat is exchanged between outside ambient air and the refrigerant. From the condenser, the refrigerant passes to an expansion device, at which the refrigerant is expanded to a lower pressure and temperature, and then to an evaporator (or an indoor heat exchanger). In the evaporator, heat is exchanged between the refrigerant and the indoor air, to condition the indoor air. When the refrigerant system is operating, the evaporator cools and typically dehumidifies the air that is being supplied to the indoor environment.
One of the options available to a refrigerant system designer to enhance the system performance is a so-called economizer cycle. In the economizer cycle, a portion of the refrigerant flowing from the condenser is tapped and passed through an economizer expansion device and then to an economizer heat exchanger. This tapped refrigerant subcools a main refrigerant flow that also passes through the economizer heat exchanger. The tapped refrigerant leaves the economizer heat exchanger, usually in a vapor state, and is injected back into the compressor at an intermediate compression point. The main refrigerant is additionally subcooled after passing through the economizer heat exchanger. The main refrigerant then passes through a main expansion device and an evaporator. This main refrigerant flow will have a higher cooling potential due to additional subcooling obtained in the economizer heat exchanger. The economizer cycle thus provides enhanced system performance. In an alternate arrangement, a portion of the refrigerant is tapped and passed through the economizer expansion device after being passed through the economizer heat exchanger (along with the main flow). In all other aspects this arrangement is identical to the configuration described above.
Recently, the assignee of the present invention has developed a compressor wherein the economizer injection port in the compressor is also utilized to provide the unloader function. An unloader line contains an unloader or bypass valve, and selectively communicates fluid from compression chambers into a suction line. Since the unloader line communicates with the intermediate compression chambers, the effect is to allow partially compressed refrigerant from these compression chambers to pass through the same injection ports and then back to suction. This action is taken to reduce capacity of the refrigerant system. This invention has many benefits, not the least of which are the elimination of separate fluid lines for each of the two functions and utilization of a single intermediate compressor port.
However, this invention has not provided as much flexibility in design as would be desirable. In particular, often the most efficient operation for the economizer function is when the fluid is injected into the intermediate compression pockets while the injection port being of a fairly small size. For this mode of operation, when the fluid is injected into the intermediate compression pockets, if the injection ports were larger then needed, then additional losses would occur, as the refrigerant would be allowed to move in and out of the compression pockets during the injection process. This undesirable movement of the refrigerant introduces additional so-called “sloshing” losses. These “sloshing” losses can reduce the efficiency of the economizer cycle. In other words, if the injection ports are too large for the injection process then there is not enough flow impedance placed in the injection port for optimum operation.
On the other hand, when the unloading mode is engaged its effectiveness is increased when the size of the port is selected to be as large as practically possible. In other words, one needs to reduce the amount of flow restriction in this unloaded mode as much as practically possible for most efficient operation in this mode. Therefore, for optimum operation, one needs different flow restrictions for vapor injection mode and for the unloaded mode. In the past, however, since the restriction was located in the same passage for both economized (vapor injection mode) and unloaded mode, the flow impedance was identical for both economized (vapor injection) and unloaded modes of operation. Therefore, it would be desirable to remove this constraint of having the same fluid restriction for both modes of operation. If this constraint is removed, then one can optimize the size of restriction for the economized operation, while at the same time make the flow as unrestricted as possible for the unloaded operation. In this case, one can substantially improve the cycle efficiency in both economized and unloaded modes.
Thus, the prior art, as for example described in U.S. Pat. No. 5,996,364 and United States pending application 20040184932, which utilize the same injection ports (that serve as a restriction) located in the common passage for both economized and unloaded function, could not fully achieve a desired result.